Drinking, waste, or industrial water is currently treated with halogens whose oxidizing biocidal and disinfecting action is well known. With regard to drinking water, the most common disinfection treatment is with chlorine and by-products thereof.
Chlorine has a strong biocidal action and residual free chlorine is usually maintained in water supplied to consumers to ensure that harmful bacteria are destroyed before the water reaches its destination.
Unfortunately, during the complex reactions which occur between the chlorine and organisms and organic pollutants various chloramines and other noxious products are formed whose biocidal action is weaker than chlorine or not biocidal at all, and these tend to leave a disagreeable smell and taste in the water. In addition the production of chloramines and other chlorinated products results in the requirement that additional chlorine must be added to the water in order to maintain the desired residual free chlorine required to destroy bacteria.
Presently within the art there are a few methods which have proposed a combination of two disinfecting species wherein one is used as a chemical reagent (not a disinfectant) whose sole purpose is to regenerate biocidal forms of the second species from spent forms of the second species. Examples of these where the two halogens chlorine and iodine are used, are U.S. Pat. No. 2,443,429 issued June 15, 1948 in the name of H. C. Markes et al and U.S. Pat. No. 3,975,271 issued Aug. 17, 1976 in the name of B. Saumier. In the case of these two prior patents the halogen chlorine or its partially reacted forms such as HOCl and NHCl are introduced to oxidize iodide to biocidal iodine (I.sub.2) which reacts with bacteria and is so reduced to I.sup.- at which time more chlorine is introduced to re-oxidize the iodide back to biocidal iodine in order to allow the process to be repeated.
In each of these systems the stated purpose of the invention is to lower the cost of biocidal iodine (I.sub.2) by reoxidation and re-use: both cases use the biocidal properties of iodine, not of the oxidizer. However, these methods require levels of iodine to be present in the water well above those generally considered physiologically acceptable for continuous human consumption, as only these high levels of iodine are sufficiently biocidal for use as disinfectants. (Minimum levels of biocidal iodine normally deemed acceptable for water treatment purposes in Canada and the United States are 0.5 mg/l to 10 mg/l depending on the condition of the water and also the volume to be consumed daily by humans over a period of time).
Also it has been found that in systems using chlorine to regenerate or reoxidize iodine to biocidal forms, significant bacterial growth takes place that would not normally be found in this amount of chlorine or iodine used alone (see Favero et al, Survival of Pseudomonas in an Iodinated Swimming Pool Applied Microbiology, Vol. 14, p. 627, 1966).
The present invention overcomes these disadvantages by employing a BZ reaction in which a minor bistable iodine system at levels below those found physiologically unacceptable for human consumption is coupled with a major bistable chlorine system by the presence of microbial life or their metabolic by-products into an active disinfecting BZ reaction which enhances chlorine's biocidal ability.
In recent years the phenomenon of oscillating chemical reactions, more commonly known as BZ (for Belousov-Zhabotinsky) reactions, has been recognized. The BZ reaction has been recently described by Epstein et al in an article in the publication Scientific American, March 1983, p. 112, in which three basic conditions were laid out as requirement for designing a chemical oscillator. The first condition is that the chemical system must be far from equilibrium. The second condition is feedback; in other words some product of a step in the reaction sequence must exert an influence on its own rate of formation. The third condition is that the chemical system must exhibit bistability, meaning that under the same set of external conditions the system must be able to exist in two different stable steady states. These reactions to date have not found any type of useful application.
The present invention overcomes the aforesaid disadvantages in the prior art by maintaining a physiological acceptable concentration level of iodine to persons consuming the water who have an iodine deficiency, or who have adequate dietary iodine. The present invention also reduces the presence, in water treated with chlorine, of combined chlorines such as chloroform and chloramines which cause bad taste and an odour. Furthermore the present invention enhances the biocidal strength of chlorine by allowing low levels of chlorine to kill bacteria that would otherwise be immune.
When the organic content of water is particularly high at some point in the system, for example due to bacterial colonization on the inner walls of the pipe carrying the water, it may be impossible in present practice to disinfect the water so that it is suitable to drink. Chlorine at levels acceptable for potable water is not always capable of killing all forms of microbial life although it is generally capable of killing organisms of public health concern. Chlorine resistant organisms such as autochemotrophic or hetrotrophic organisms colonize on pipe walls and form organic slimes which remove chlorine from the system, rendering the amount of chlorine which is generally considered acceptable to introduce during treatment, insufficient to make the water supply contain residual free chlorine.
To meet this problem of the buildup of bacteria and their by-products on the inner walls of pipes, the present method of removing bacterial colonization debris is through the physical method of pigging and/or swabbing.
It is an object of the present invention to provide a BZ reaction using chlorine and iodine to disinfect the inner walls of pipe or to disinfect other solids using a continuously flowing fluid containing this BZ reaction.